The invention relates to an apparatus for analyzing liquid samples automatically and continuously by mixing certain reagents with the use of membrane pumps, mixing chambers and conduits and evaluating the reaction results with the help of suitable sensors.
In the state of the art, apparatuses are known which use, for this task, different types of pumps, including also membrane pumps, which deliver a certain volume in a particular time and, with that, bring about the mixing ratio necessary for the chemical reaction.
Furthermore, pump arrangements are known which mix particularly small amounts of reagents. Manufacturing technologies are used for this purpose which can be considered to be in the field of micromechanics. The active element is a micropump, which is responsible for delivering the sample or a reagent necessary for the analysis. This micropump consists of a driving mechanism and a valve arrangement.
In Gerlach and Warmus, Technical University Ilmenau, Design Considerations on the Dynamic Micropump, ACTUATOR 96, 5th International Conference on New Actuators, Jun. 26-28, 1996, Bremen, Germany, a membrane in a silicon wafer, which is constructed as a piezo dimorphic system, is used as driving mechanism. The valves are direction-dependent, pyramidshaped flow resistances, which are disposed in a second silicon wafer. The use of two wafers, which must be positioned precisely and are connected to one another, is a disadvantage. Due to tolerances, the metering of precise amounts is not achieved.
A different construction, described in Buestgens et al., Micromembrane Pump Manufactured by Molding, ACTUATOR 96, 5th International Conference on New Actuators, Jun. 26-28, 1996, Bremen, Germany, uses as valve an elastic membrane, which is clamped between two carrier plates. The propulsion is accomplished in this case by heating and deformation. The need to manufacture several carrier parts, which must be joined together accurately positioned, is a disadvantage here also. The heating of the membrane represents a limitation for certain reagents. The amount delivered can also be controlled only with difficulty.
An arrangement, described in Temmel et al., A Micromechanical System for Liquid Dosage and Nebulization, ACTUATOR 96, 5th International Conference on New Actuators, Jun. 26-28, 1996, Bremen, Germany, also uses several individual parts which must be joined together positionally accurate with respect to one another. The system is driven by electrostatic forces which deform a membrane. The valves are constructed as gates which produce a direction-dependent flow resistance. The amount delivered is controlled. The expensive manufacturing process, especially when an arrangement with several dozen pumps is being considered, is also a disadvantage.
It is, therefore, an object of the invention to provide an apparatus for analyzing liquid samples automatically and continuously, which is defined by a large number of pumps, valves, mixing and reaction chambers in the same shaped part, which can be produced with high precision.
This objective is accomplished owing to the fact that a structure is provided in a silicon wafer of 100 orientation by anisotropic etching which, together with a glass covering layer mounted by anodic bonding, results in an arrangement of pumps, valves, mixing chambers and reactors. As a driving mechanism, the pumps use a piezo dimorphic system which is formed by mounting a piezo plate or a piezo-active layer on the glass covering layer or on the bottom of the pump chamber.
The pump chamber is rectangular with a trapezoidal cross section. Directly in front of and behind the pump chamber there are conduits of a triangular or trapezoidal cross section which present a nonlinear flow resistance. The mode of functioning is that, up to a certain flow velocity v, laminar flow exists and, when this flow velocity is exceeded, this laminar flow changes over into turbulent flow. With that, there is a sudden change in the flow resistance.
The geometry of the inlet and outlet ducts is different, so that the point at which linear and nonlinear flow sets in is different. If now the membrane is deflected with a steady pulse, the amplitude of which changes with the duration, the times at which there is a changeover from laminar to turbulent flow are different in the inlet and outlet ducts. With that, a direction-dependent flow resistance results over average time and brings about a volume flow over the whole of the arrangement. The volume flows in the one direction or the other, depending on whether the pulse is increasing or decreasing over time. For metering precisely the amount of liquid delivered, measurement conduits, adjoining the pump chamber and representing a defined flow resistance, can be accommodated in the silicon wafer. Liquid pressures, arising at the two ends of the measurement conduit, are a measure of the amount flowing through the measurement duct.
The pressure difference can therefore be used as a variable for regulating the pump frequency or the pump amplitude in order to adjust the amount delivered precisely. Several pumps can act at the outlet side on a common chamber which, corresponding to the manufacturing technology for the 100 oriented silicon wafers, is also configured rectangularly with a trapezoidal cross section. Due to the asymmetric inlet into this chamber, swirling of the various reagents takes place. With that, mixing and a stable chemical reaction are produced.
The mixing chamber can be used as a common reference potential for measuring the pressure or the flow through the apparatus. The outlet side of the mixing chamber is connected by means of a conduit with the reactor, which also has a v-shaped or trapezoidal cross section. The flow rate and the conduit length can be designed so that the reaction time is sufficient for evaluating the liquid by suitable sensors. With that, quasi continuous measurement is possible.